1. Field of the Invention
The present invention generally relates to a display apparatus, and more particularly, to a liquid crystal display (LCD) apparatus having copper electrodes.
2. Description of Related Art
The rapid development of a multimedia society mostly results from the fact that semiconductor elements or human-information display apparatuses have progressed by leaps and bounds. Among the display apparatuses, flat panel displays featuring superior characteristics of high definition, great space utilization, low power consumption, and non-radiation have gradually become mainstream products in the market. At this current stage, a thin film transistor liquid crystal display (TFT-LCD) is the most mature flat panel display. Specifically, an electrode lead line of great quality plays a key role in equipping the TFT-LCD with specific characteristics so as to comply with current demands on great dimension and high-resolution of the TFT-LCD.
Among various materials constituting the electrode line, copper is characterized by low resistivity, low coefficient of thermal expansion, high melting point, great thermal conductivity, high anti-electromigration, and so forth. Moreover, copper lines are able to approximately double the performance of TFT devices in comparison with aluminum leads. As long as the lines are made of copper, not only an RC delay can be minimized, but also electrostatic capacity between the copper lines can be reduced. As such, copper has become one of the most imperative conductive materials constituting the electrodes and the leads.
Since copper is not able to form a self-protective oxidation layer under an atmospheric environment, the copper lines are likely to be oxidized and corroded in a conventional manufacturing process of a pixel structure having the copper lines. In addition, the TFTs using copper as the electrodes are often deteriorated due to certain properties of copper. For instance, an adhesion between a copper electrode and a substrate is relatively unsatisfactory. Further, silicide may be formed by copper and silicon under a low temperature. Besides, copper has a high coefficient of diffusion in a dielectric layer. In light of the foregoing, the pixel structure using copper as the electrodes or the leads encounters practical challenges.
In general, as the material of a source and a drain of the TFT includes copper, a conventional pixel structure using copper as the electrodes has been proposed to avoid copper from being in direct contact with an active layer, an ohmic contact layer, and the dielectric layer (i.e. a gate insulating layer). In the TFT having said conventional pixel structure, a copper oxide layer serving as a barrier layer is often disposed between a copper layer and the active layer and between the copper layer and the dielectric layer, such that copper can be prevented from being diffused into the active layer. Additionally, the copper oxide layer is also conducive to promoting the adhesion between the copper layer and the substrate. It should be noted that an upper electrode of a storage capacitor of the pixel structure is made of copper as well. Moreover, the copper oxide layer as the barrier layer is required to be disposed between the copper layer and the dielectric layer for blocking copper from being diffused into the active layer and for enhancing the adhesion between the copper layer and the substrate.
Nevertheless, in a subsequent process of manufacturing said pixel structure, the direct contact between the copper oxide layer and the dielectric layer brings about a reduction of the copper oxide at or around an interface between the copper oxide layer and the dielectric layer due to reactive gases generated in the subsequent process. Thereby, the copper layer may be peeled off, or bubbles may be generated, as illustrated in FIGS. 1A and 1B. Aside from the above-mentioned reduction of the copper oxide, the reactive gases may be further diffused to the copper oxide at or around the interface of the copper oxide layer and the active layer and/or the ohmic contact layer, resulting in the peeling-off of the entire copper layer or the generation of the bubbles. Here, the subsequent process is, for example, a process of fabricating a passivation layer in which a chemical vapor deposition (CVD) process is performed for forming a silicon nitride film layer. Gases adopted in the process include the reactive gases (e.g. silicon-containing gases, nitrogen-containing gases) and carrier gases. For instance, the silicon-containing gases include silane, disilane, trisilane, tetraethyl orthosilane (TEOS), tetra-silane, other gases, or combinations thereof. The nitrogen-containing gases include nitrogen, ammonia, other gases, or combinations thereof. The carrier gases include nitrogen, oxygen, helium, neon, argon, krypton, xenon, radon, other gases, or mixture gases selected from the above gases. It should be noted that the passivation layer made of different materials gives rise to the production of different reactive gases and different carrier gases, and all of the gases cause the aforesaid problems. FIG. 1A is a schematic view illustrating a partial region of the pixel structure in which the bubbles are generated in the copper layer according to an observation result obtained by an optical microscope. Referring to FIG. 1A, a copper electrode 12 made of copper generates bubbles B in the subsequent process. FIG. 1B is a schematic view illustrating a partial region of the pixel structure in which the copper layer is peeled off according to an observation result obtained by an electron microscope. Referring to FIG. 1B, a copper electrode 22 is peeled off from a bottom layer 21, such that an upper film layer 23 disposed on the copper electrode 22 is also peeled off. As shown in FIG. 1A, the copper electrode 12 serving as the line is peeled off in the subsequent process because of the production of the bubbles B. Therefore, it is a to-be-resolved crucial issue for the copper electrode and the copper line to be applied to the manufacturing process of the pixel structure.